Mumps, which got its name from an Old English word meaning grimace, is also caused by a virus. The incubation period is 12 to 25 days, but 20 to 40 percent of those infected show no symptoms. In 1964, 213,393 cases of mumps occurred in the United States. Today there are between 4,500 and 13,000 cases per year.

When a person infected with mumps does have symptoms, they include a low-grade fever and swelling or tenderness of one or more of the salivary glands in the cheeks and under the jaw. The pain is often worse when swallowing, talking, or chewing. Loss of appetite is also common.

The disease is contagious from three to four days before to four days after symptoms appear. Between 20 and 40 percent of infected people do not have symptoms of mumps. Although mumps doesn't usually cause long-term problems, some of the symptoms, like severe swelling of the salivary glands, can be very uncomfortable. Women may be at risk for spontaneous abortions if they get mumps while pregnant. Mumps is spread from person-to-person through direct contact with saliva, coughs and sneezes, and urine of an infected person.

Child with mumps. (Courtesy CDC/Patricia Smith, Barbara Rice)

Fortunately, mumps is preventable with the MMR vaccine, which is discussed later in this section.